Electronic cigarettes are supposed to be the safer way to get your nicotine fix. But old fashioned cigarettes don't explode in your pocket or blow up in your face. And that's what's happening across the country with some e-cigarette batteries.

Thankfully, these mishaps don't happen very often, but when an e-cigarette battery malfunctions, the injuries can be horrendous — burns on the hands and face, fractured bones and loss of eyesight.

"It's literally an explosion, a super-hot explosion," said Dr. Anne Wagner of the University of Colorado Hospital (UCH) Burn Center, where they've treated six people seriously injured by e-cigarettes since the beginning of the year. "We're seeing deep third-degree burns and almost all of them require skin grafts and these grafts leave a significant scar."

Earlier this year, the UCH Burn Center treated 19-year old Alexander Shonkwiler after an e-cig battery exploded in his pocket, set his pants on fire and caused a painful burn on his upper thigh.

"I heard what sounded almost like a sparkler going off, and then bang, a huge explosion, a huge flash of light and these flames were coming at my face," Shonkwiler said. "As I looked down, my leg was on fire. I ripped my pants off, and even with my pants off, my leg was still on fire because the battery acid sprayed all over my leg and dripped down my leg."

Shonkwiler told NBC News he'd taken the battery out of the device and had it in his pocket with some coins. That could have resulted in a short. He said the package didn't warn about the hazard, and he never realized the risk.

Despite the potential for danger, e-cigarettes are currently an unregulated product, so we don't know how many injuries they've caused.

The only statistic available is from a 17-month old report from the U.S. Fire Administration that found 25 e-cigarette injuries between 2009 and 2014. The report noted that the shape and construction of e-cigarettes can make them more likely than other products with lithium-ion batteries to behave like "flaming rockets" when a battery fails.

The Fire Administration estimated that more than two-and-a-half million Americans used e-cigs in 2014, a practice known as vaping. The industry says the number of people who have switched from smoking to vaping has grown dramatically in the last two years. So have the mishaps.

"We initially thought this was a rare event, but this is increasing in frequency," said Dr. Elisha Brownson, a trauma and burn critical-care fellow at Harborview Medical Center in Seattle. The burn unit at Harborview is now treating one e-cig-related injury a month, five since October.

"We're seeing significant tissue injury as well as damage to the mouth or the hands and the tendons," Dr.Brownson said. "It basically combines a flame burn and a tissue blast injury."

Ray Story, CEO of the Tobacco Vapor Electronic Cigarette Association (TVECA), said his members are "devastated" when they hear about these accidents and injuries. But, he pointed out, "millions and millions of people are using these devices and there have only been a few accidents."

"When you lack regulatory oversight, then it basically becomes a free-for-all," Story told NBC News. "When opportunistic companies find themselves in a position where they can make a quick buck, caution is out the window, so they purchase batteries and equipment that clearly is not up to snuff."

TVECA supports what Story calls "logical and responsible regulation and oversight." He said regulation would require every company to follow good manufacturing practices and provide customers with important safety information.

Why is this happening?

There doesn't seem to be a single reason for these failures. Some of the obvious problems include the lack of industry-wide manufacturing standards or testing programs, and misuse by vapers who modify their devices or use the wrong battery chargers.

The lithium-ion batteries used to power e-cig vaporizers are small and powerful. When they fail, the results can be disastrous. We've seen that with cellphones, laptops and most recently, hoverboards.

An e-cig is a fairly simple device. A heating element vaporizes the liquid solution (the "juice") in the atomizing cartridge. Some have an on/off switch; others heat automatically when the user takes a drag.

"The electrolyte inside the battery is basically the equivalent of gasoline," explained Venkat Viswanathan, an assistant professor of mechanical engineering at Carnegie Mellon University. "So when these batteries short out, there's a surge of heat that causes this flammable electrolyte to combust and explode."

Well-made lithium-ion cells have a very small risk of failure. But the cheaper cells "have a much greater chance of having a manufacturing defect," which increases the likelihood for failure, Viswanathan told NBC News.

The risk goes up if the cells are overcharged or charged too quickly. This can happen if the e-cig comes with a poorly designed charger or the user switches chargers. Well-made lithium-ion batters have fail-safe mechanisms to prevent these problems. Poorly-made ones do not.

Warning: Just because a charger plugs into that e-cig doesn't mean you should use it.

Michigan attorney Steven Weston points out in a recent National Law Review article, these explosions can happen without warning — even when the e-cig is being used. Weston represents a young man who was driving when an e-cig exploded in his face and caused him to crash.

"The hazard is so extreme. There's not necessarily any precursor to an explosion," Weston told NBC News. "We're trying to get the word out… that if you use these things you could blow yourself up and burn yourself — right now, unpredictably, at any time."

The U.S. Consumer Product Safety Commission (CPSC) and the Food and Drug Administration (FDA) are well-aware of the problem, but neither agency currently regulates these new devices. CPSC's National Injury Information Clearinghouse database has 29 reports of house fires and serious injuries caused by exploding e-cigarettes.

The FDA wants the authority to regulate electronic cigarettes. It's been waiting for approval from the Office of Management and Budget (OMB) since October. Because of that, the CPSC is not getting involved. The FDA is taking e-cig complaints on its Safety Reporting Portal.

Sean Kane, president of Safety Research & Strategies, Inc., told NBC News he is "troubled" that no federal agency is regulating e-cigs. And because of that, manufacturers do not have to report safety defects that could create a hazard or injuries, if they happen.

"We're seeing a flood of these low-cost, low-quality devices that are hurting people and we're dealing with safety as an afterthought," Kane said. "We need tough standards that require good design and manufacturing practices to ensure these devices are produced safely."